Catalytic cracking of hydrocarbon oils



May 18', 1943 STABILIZER FRACTIONATORS REACTORS FIG. l

Du Bols l-:As'rMAN ETAL "2,319,590

ATALYTIC GRACKING OF HYDROCARBON OILS 5 Sheets-Sheet l Filed Jan. 13,1940 COOLER & CONDENSER HEATER FUEL AGAS RECEIVER DU BOIS EASTMANCHARLES RICHKER YAM 5W THEIR ATTORNEYS -May 18 1943 DU Bols EAsTMAN ErAL2,319,590

CATALYTIC CRACKING OF HYDROCARBON OILS Filed Jan 13, 1940 5 Sheets-Sheet2 FIG. 3

LENGTH OF' PROCESS CYCLE -HOURS l l O O O o v m BNOSV) SVI-ld SVD-NOISHBANOD Z: 1M

LENGTH oF PROCESS CYCLE -HouRs F IG.

o oni Bols EAsTMAN CHARLES RICHKER BY mf@ May 18, 1943 DU BOIS EASTMANETAL CATALYTIC CRACKING OF HYDOCARBON OILS Filed Jan. 13, 1940 "54Sheets-Sheet 3 LENGTH OF PROCESS CYCLE'. -HOURS Du Bols EASTMAN CHARLESRICHKER INVENTORS sra/M THEIR ATTORNEYS Patented May 18, 1943 2,319,590CATALYTIC CRACKNIESOF HYDROCARBO DuBois Eastman and Charles Rlchker,Port Arthur, Tex., assignors, by mesne assignments. to The TexasCompany, New York, N. Y., a corporation of Delaware Application January13, 1940, Serial No. 313,654 11 Claims. Cl. 1516-52) This inventionrelates to the catalytic cracking of heavier hydrocarbon oils to convertthe same to gasoline hydrocarbons suitable for motor and aviation fuel.

One of the principal objects of the invention is 4to provide an improvedcatalytic cracking process of this character having greatly increasedconversion cycle time over such processes as heretofore commerciallyemployed, with greater throughput and capacity of the plant for lowerinstallation and operatingcosts.

Another object of the invention is to provide a catalytic crackingprocess of this character in whichthe feed stock is selected to give aclean charge and the conditions of operation correlated to provide anexceedingly long time on stream or conversion cycle time beforereactivation of the catalyst is necessary, to give a high conversion ofgasoline plus gas/per pound of carbon deposited on the catalyst. withresulting high throughput and efficiency of operation.

Other objects and advantages of the invention line hydrocarbons withconcomitant breakdown of a portion of the feed to gas and resultantdeposition of coke or carbon on the catalyst. The

activity of the catalyst as measured by the percentage conversion perpass to gasoline and gas drops off exceedingly rapidly as the carbondeposit builds up on the catalyst. In order to maintaina desirably highconversion, it has been customary to run with an exceedingly shortconversion cycle or on-stream time, then terminate the flow of thehydrocarbon charge through the catalyst bed, and reactivate that bed bypassing therethrough a highly heated gas containing air or oxygen toburn or! the carbon deposits and bring the catalyst back to a highactivity. The reactivation may be preceded by a purging of the catalystbed following the on stream time, such as by passing steam or otherinert gas through the bed; and a similar purging may be employedfollowing the reactivation period. In a typical installation of theso-called Houdry type, itis customary to employ an operating cycle often minutes on-stream, five minutes for purging, ten

minutes for reactivation, and five minutes for a final purging beforethe unit is again placed onstream. This means that a catalytic crackingchamber is orf-stream for twice the period of timel quality of product.Apparently previous results tended to confirm the prevalent belief inthe industry that continuance of the on-stream time would give aprogressive decrease in conversion, while the rate of carbon depositionon the catalyst would remain essentially constant under the givenoperating conditions. It had also been found that when excessivequantities of carbon were allowed to deposit on the catalyst bed, thereactivation of that catalyst could only be accomplished withexceedingly great diiliculty and often without a return of the catalystto the desired high activity.' Consequently. in order to obtain thedesired practical conversion per pass and the proper reactivation of thecatalyst. resort has been had to the short on-stream cycles.

Contrary to expectations and the previous knowledge in this art, it hasnow been found that greatly improved results are secured under properand controlled operating conditions by employing a conversion cycle timeor on-stream time which is increased many times over previous practice.Further, the proper reactivation of the catalyst is effected with areactivation cycle time which is not greater than, and is usually lessthan, the con-version cycle time. Greatly increased throughput andhigher efciency of operation of the plant are thereby secured. This isaccomplished by iirst selecting a suitable charging stock which is arelatively clean oil of good color. Second, a cracking catalyst of highand sustained activity is employed. And third, the operating conditionsof -temperature, pressure and space velocity are correlated with theother factors to allow prolonging the conversion cycle time to a periodin excess of four hours, and preferably of the order of 8-20 hours ormore. Under these conditions, the catalyst with deposited carbon or cokeat the termination of the on-stream time can be reactivated withoutdifliculty with a reactivation cycle time not greater than four hours,and generally of the order of 2-3 hours.

Under these operating conditions, a further unexpected result has beenobtained. This is that the conversion rate per pass drops off only acomp'aratively small amount as the conversion cycle time is prolonged towithin the range set forth above, while the rate of carbon deposition onthe catalyst falls olf a comparativelyrlarge amount. Thus there isobtained a conversion yield in excess of fifty pounds, and generally ofthe order of eighty pounds or more, of gasoline plus gas per pound ofcarbon deposited on the catalyst. This is greatly in excess of theconversion yields per pound of carbon deposited on the catalystheretofore obtained with the conventional short operating cycle. At thesame time, the ratio of gasoline to gas produced is maintained at adesirably high figure, and the quality of the gasoline is at least asgood as that produced with the short operating cycle.

In accordance with the present invention, a heavier hydrocarbon oil feedstock is -selected which is of clean character and good color, asrepresented by a carbon residue of less than 0.2% and a color of lessthan 200 as measured on the Lovibond 1/2" scale. Various types of feedstocks having these characteristics can be employed, such as variouskerosenes, gas oils, distillate lubricating oils and even topped crudesand residuals, which have been treated to bring them within thecharacteristics mentioned above. Either straightrun, cracked or cyclestoc :s` or mixtures thereof, can be employed, although it is generallypreferred to utilize straightrun fractions. A stock relatively free fromunsaturates is preferred, and this stock may be from paraffinic, mixedbase or naphthenic crudes, although the fractions from naphthenic crudesappear to give even better results. From the operating standpoint, astraightrun gas oil, either light or heavy, or a broad range fraction,representing normal plant supply, is emin tly satisfactory.

The type of catalyst empl ed may be deilned as one having high initial awell as sustained activity, such'as a catalyst giving a conversion perpass in excess of and preferably in excess of 25%, by weight ofgfasoline plus gas over a processing cycle in excess of four hours, andpreferably of the order of 10-20 hours or more. Various catalystssatisfying these requirements under the present conditions of operationhave been found, and the invention is applicable to any active crackingcatalyst of this type. As representative of the catalysts satisfyingthese requirements, there may be mentioned the synthetic silica-aluminatype. Various acid-treated clays such as the Super-Filtrols andmetal-substituted clays, are satisfactory. Likewise, the acid-treatedand metal-substituted natural or artificial zeolites, such as theartificial zeolite known as Doucil, can be used. Various metals can besubstituted in the clays or zeoiites, such as uranium, molybdenumL,manganese, lead, zinc, zirconium, nickel and the like. Likewise, thecombination of certain acid-treated active clays of the character ofFiltrol, together with added proportions of alumina*v or silicate orboth can be employed. Alumina alone may be used under certainconditions. The synthetic silica-alumina catalysts can be improved bythe addition of other constituents, such as zirconium oxide ormolybdenum oxide. Other catalysts which are not silica-aluminacatalysts, either synthetic or prepared from natural minerals, have beenfound which satisfy the characteristics of the catalyst of the presentinvention. In general, a catalyst is employed which is stable at hightemperatures of the order of.1400-1600 F., as determined by calcining ina mufile furnace at that temperature,

During the processing cycle, the catalyst is' 'maintained at atemperature of 850-1050 F.,

and preferably of the order of S10-1000* F. Pressures of the order ofatmospheric up to about 200 pounds per square inch may be employed, butitis important that the pressure be correlated with the temperature sothat the pressure is below the critical or dew point of the charge stockat the temperature used, whereby the preheated. and v aporlzed oilcharge is maintained in completely vaporized form in contact with thecatalyst and oil deposition or condensation on the catalyst is avoided.For example, with a temperature of 850 F., a pressure of about fiftypounds per square inch is approximately the critical pressure, andconsequently somewhat lower pressures than this are generally employedat the lower temperatures. 'I'he intermediate or higher temperatureswithin the range specified are therefore preferred. The higher pressuresof operation are preferred for thermal economy, particularly in thefractionation of the cracked products; and consequently the pressure isgenerally raised to approach but be below the critical pressure for thetemperature employed.

The charge rate during the processing cycle is conveniently expressed interms of space velocity, which means the total liquid volume of chargedivided by the total volume of catalyst (solid volume plus voids) perhour. Expressed in these units, a space velocity of about 1-10 givessatisfactory results, and about 3-6 is preferred. In determining spacevelocity the liquid charge is usually regarded as liquid measured at 60F.

During the reactivation, a mixture of flue gas and/or steam with air oroxygen is employed. 'I'his ue gas is preheated, preferably to a tem-lperature of the order of about 800 F., and is then passed through thecatalyst bed to cause a low temperature combustion of the depositedcarbon on the catalyst. The temperature of the catalyst during thereactivation is maintained below a certain peak temperature as measuredby thermocouples positioned within the catalyst bed, which peaktemperature may be of the order of 1100-1400 F. 'I'his may beaccomplished by any suitable means of cooling or extracting heat fromthe catalyst during the reactivation, and may be at least in partcontrolled by the oxygen .content of the flue gas which is generallyofthe In the annexed drawings, which illustrate a preferred embodimentof the invention:

Fig. 1 is a flow sheet of a catalytic cracking plant for carrying outthe method of the present invention;

Fig. 2 is a diagram illustrating a. typical curve of the weightpercentdeposit of carbon on the catalyst for various processing cycletimes, based upon the weight of the charge supplied to the crackingunit: f

Fig. 3 is a diagram illustrating a typical curve of weight percentconversion per pass to gasoin the stack of furnace I3 and thence throughradiant heating coil I4-within thel furnace and line I5 to a -i-waycontrol valve I8. The latter controls the passage of the preheated andvaporized oil to one or the other of lines I1 and I8 leading into thetop of the catalystv chambers I3 and 20 respectively, Each catalystchamber is supplied with a suitable volume of an active crackingcatalyst of the type hereinbefore mentioned, and may be equipped withany suitable means (not shown) for maintaining and controlling thetemperature of the catalyst during the processing and reactivationcycles.

As shown, the valve I6 is in position to conneet lines I5 and I8 so thatthe oil charge passes into catalyst chamber and flows downwardlytherethrough for the conversion operation. The

oil charge is preheated to a temperature to be maintained within thecatalyst bed, and may be heated to a somewhat higher temperature inorder to supply additional heat thereto and make up for heat losses fromthe catalyst chamber. The gaseous conversion products are dischargedfrom the base of the catalyst chamber 20 through line 2l communicatingwith 4-way control valve 22, which also controls communication of line23 leading from the base of catalyst chamber I3 with a discharge line 24which empties into a rst fractionating tower 25. y

Tower 25 operates to fractionate the vapors and to condense heavybottoms or cycle fuel oil which is discharged from the base of the towerthrough line 26. The gaseous vapors including gas, naphtha andunconverted gas oil pass overhead through line 21 to a secondfractionating tower 28 where the clean recycle stock or gas oil iscondensed and withdrawn by line 29 for recycling to the charge line o rother suitable disposal. Vapors of naphtha and gas pass overhead fromtower 28 through line 30 to a condenser and cooler 3l and into anaccumulator drum 32. From the latter, condensed liquid is withdrawnthrough line 33 and forced by pump 34 through line 35 into astabilizingtower 36. Vapors separating in accumulator drum 32 arewithdrawn through vapor line 31 and forced by pump38 through line 39which discharges into line 35, whereby the liquids and vapors from theaccumulator drum are introduced together into the stabilizer 35.

Stabilizer 3B is operated to condense the naphtha therein, which may bewholly or partially debutanized butpreferably retains a portion of thebutane to improve volatility. 'I'his naphtha, v

livered for further processing.

Flue gas for reactivation may be obtained from any suitable source. Asshown, it'is produced in a flue gas generator 45. vA.suitable-combustible gas such as natural gas or refinery gas from supplyline 45 is forced by compressor 41 into fuel gas receiver 48, fromwhence itis led by line 43 to suitable burners 50 discharging into thecombustion space within generator 45. A line 5I carrying high pressureair leads to burners 50 to supply air for combustion. The products ofcombustion or flue gases at high temperature and under pressuredischarge from generator 45 through line 52 into a suitable scrubber 53,where the gases are purified. The clean flue gas then passes by line 54to one of lines 55 and 55 under the control of valves 51 and 58respectively. Line l55 contains a heating coil 53 positioned within thecombustion space of generator 45. By suitable regulation of theproportions of the flue gas passed through lines 55 and 56, thetemperature of the gas is controlled. Additional air from line 5I isintroduced by branch line v6I) into line 55 to control the oxygencontent of the reactivating ue gas. This mixed gas at a temperature ofabout 800-900 F. is introduced by line 5I and` control valve I5 intoline I1 and passes downwardly through the catalyst within catalystchamber I9 for the reactivation. The resulting gas, after passingthrough the catalyst bed, is discharged by line 23 through control valve22 into line 62 which leads the gas to a stack or other suitable pointof accumulation such as a gas holder, for recycling.

While in the drawings there is shown, as a matter of convenience, twocatalyst chambers, it is tolbe understood that any su-itable number maybe provided, whereby oneor more of the catalyst chambers can be carryingout the processing cycle while the remaining chamber or chambers can becarrying out the reactivation cycle, whereby the process is continuous.`yIn accordance with the present invention, where a processing cycle timesubstantially in excess of the reactivation cycle time is obtained, itis convenient to provide a series of catalyst chambers so that one maybe reactivating for a comparatively short time while the remaining onesmay be on-stream in the processing cycle for a comparatively longertime.

For example, in the case where a Iprocessing cycle time of 20 hours isemployed with a reactivation cycle time of approximately 4 hours orsomewhat less, five catalyst chambers may be used -for processing whileone is reactivating. At lthe completion of the reactivation period forthis one catalyst chamber, it is then thrown back on the line forprocessing, while one of thev other catalyst chambers which was thefirst of the group to be placed on-stream is then taken off the line andplaced on reactivation. It is to be under stood, however, that wherehigh plant capacity is not a desideratum, a fewer number of catalystchambers can be employed, such as the two that are shown, and whereinthe reactivation of the catalyst chamber oil-stream is carried out onlyintermittently and with a substantially shorter period than theprocessing cycle in the other chamber.

.After a catalyst chamber is taken olf-stream,

' it is found desirable to first flush the catalyst with flue gascomparatively free of air or oxygen for a short period. After' this isaccomplished, air is gradually bled into the ue gas to bring the oxygencontent of the gas up to the percentag'e desired, and it is then heldconstant for the duration of the reactivation cycle. Before the chamberis again placed on-stream. the catalyst bed is preferably purged by'flushing with ilue gas, the air .bleed having in the meantime been cutolf. During the reactivation, the temperature of the catalyst bed tendsto rise due to the combustion taking place therein, and this iscontrolled so as to stay below a peak temperature, such as to avoidinjury to the catalyst, as by cooling or absorbing heat from thecatalyst bed in any suitable manner. When the reactivation issubstantially complete, the temperature of the bed drops to approach thetemperature of the entering iiue gas, which is an indication that thecatalyst chamber is again ready to be placed ori-stream.

Fig. 2 is a typica-l'curve illustrating the weight percent, based on thecharge, of carbon deposited on the catalyst for various lengths oi. theprocess cycle in hours, where the conditions of operation remainotherwise uniform' as to temperature, pressure, space velocity, etc. Itwill be noted that for short processing cycles up to approximately 4hours, the weight percent of carbon is relatively large, and drops on ona steep curve or quite rapidly as the processing cycle is increasedwithin that range. Beyond 4 hou'rs processing cycle time the curveflattens out somewhat but further appreciable reduction in the carbondepowhere the process cycle isincreased to 8 hours or more.

- Obviously many modifications and variations 'of the invention ashereinbetore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

We claim:

i. 1n the catalytic cracking of a normally liquid less than 200 on theLovibond V2" scale through a contact mass of active cracking catalystmaintained at a temperature of about 910 to 1000 F.

at a space velocity of 3 to l0 for a conversion period in the rangeabout four to twenty hours sition rate takes place as the processingcycle time is increased to 15 hours or more.

Fig. 3 illustrates a typical curve for the weight percent, based on thecharge, of conversion to gasoline plus gas forY varying lengths of theprocess cycle in hours, where the conditions of operation remainotherwise uniform. As shown, the

vconversion falls rather rapidly for extremely positeu on the catalystis plotted against tile length o1 the process cycle m hours ior variousweight percentage conversions o1' the charge to gasoline plus gas. 1twill be noted that tne various weight percentage conversioncurves areessentially straight lines with an appreciable slope. Uovlousiy, theconditions or operation would have to oe altered during tne'continuanceoi a ruxi to produce a constant conversion rate or zum), .50%, w70,etc., throughout the run. This ls not done ni practice. '.lhe curves.herein shown were prepared Irom data assembled Irom cliierent runs olithe same charge stock and with the saine catalyst, giving at least twopoints on each conversion curve, winch is surlcient to determine thelocation and slope of the straight line. l'nis indicates the advantageoi' increasing me length or the process cycle I'or any set oi' operatingconditions which will give the percentage conversion indicated. .rorexample, an operation giving a 20% conversion under the conditions o1'this invention will give about 0.15% by weigllt or carbon deposited onthe catalyst for a i-hour processing cycle, and approximately 0.10% ofcarbon for an 8-hour processing cycle. For more rigorous operatingconditions where a 30% conversion is obtained, less than 0.20% by Weightof carbon will be deposited on the catalyst on stream, to obtain aconversion'. to gasoline plus gas of not less than 50 pounds per poundof carbon deposited on the catalyst, the ratio of gasoline plus gas tocarbon being produced-when the catalyst has lbeen onstream 4 hours ormore, being substantially greater Vthan that obtaining during a periodof less than 4 hours, then discontinuing the ilow of thehydrocarboncharge in contact with said catalyst after substantial deposition oilcarbon upon the catalyst, reactivating the catalyst in situ in a periodof time less than the said conversion period, and then repeating theprocess.

2. The method as deilned in claim 1. in 'which the catalyst vis asynthetic vsilica-aluminazirconia catalyst. 3. The method as dened inclaim' 1, in which the conversion cycle time is in excess oi.' eighthours, and the reactivation cycle time is less than four hours.

, 4. The method as deilned in claim 1, in which a conversion pressure ofatmospheric to 200 pounds per square inch is employed, and in which thepressure is correlated with the temperature so as to approach butbebelow the critical pressure for the temperature employed to maintainthe charge stock. completely vaporized and to avoid oil condensation onthe catalyst.

5. The method as defined in claim 1, in which the charge stock is astraightrun gas oil, the conversion temperature of the catalyst is 910to 1000 F., the pressure employed is such as to maintain completevaporization of the charge stock in contact with the catalyst, the spacevelocity is about 3 to 6, the conversion cycle time is 8 to 30 hours,and the conversion is not less y same to gasoline hydrocarbons involvingalternate periods of conversion and reactivation, the method whichcomprises continuously passing a preheated and vaporized hydrocarboncharge stock having a carbon residue of less than 0.2% and a color ofless than 200 on the Lovibond 1/2" scale through a contact mass ofactive cracking catalyst maintained at a temperature oi' about 910 tol000 F. at a space velocity of 3 to 10, continuing the now ofhydrocarbon charge.

under said conditions in contact with the catalyst for a conversionperiod in the range about 4 to 20 hours on stream, to obtain aconversion to gasoline plus gas of not less than 50 pounds per pound oicarbon deposited on the catalyst, the ratio of gasoline plus gas tocarbon being produced when the catalyst has been onstream 4 hours ormore, being substantially greater than that obtaining during a period ofless than 4 hours, thereafter discontinuing the iiow of the hydrocarboncharge in contact with the catalyst after substantial deposition ofcarbon upon the catalyst, reactivating the catalyst in situ, and thenresuming the iiow oi? hydrocarbon charge to the 'reactivated catalystunder the aforesaid conditions. Y

'7. The method according to claim 6 in which the catalyst is a syntheticsilica-alinnina catalyst substantially free from alkali metals.

8. In the catalytic cracking oi a normally liquid heavier hydrocarbonoil charge to convert the same to gasoline hydrocarbons involvingalternate periods of conversion of the oil and reactivation of thecatalyst, the method which comprises continuously passing a preheatedand vaporized stream oi hydrocarbon oil charge stock having a carbonresidue of less than 0.2% and a color of less than 200 on the Lovibond1/2 inch scale through a mass of active cracking catalyst, maintained ata temperature of 910 to 1000 F., at a space velocity in the range 3 to 6for a conversion period of about 4 hours onstream, to obtain aconversion to gasoline plus gas of at least about 50 pounds per poundcarbon deposited on the catalyst, the ratio oI-gasoline plus gas tocarbon being produced when the catalyst has been onstream 4 hours ormore, being substantially greater than that obtaining during a period orless than 4 hours, discontinuing the ilow o1 the hydrocarbon charge incontact with said catalyst aiter substantial deposition of carbon on thecatalyst, reactivating the catalyst in situ, and then repeating theprocess.

9. In the catalytic cracking o1 a normally liquid heavier hydrocarbonoil charge to convert the same to gasoline hydrocarbons involvingalternate periods oi conversion o! the oil and reactiva- Y tion of thecatalyst, wherein a vaporized feed oil, having a carbon residue of lessthan 0.2% and a color of less than'200 on the Lovibond 1/2 inch scale,at a temperature of 910 to 050 F.

and at vhigh space velocity in the range 3 and above, is continuouslypassed through an active contact mass maintained at the elevatedtemperature during said periods .of conversion, the method comprisingcontinuing the iiow of heated charge oil through the contact mass undersaid conditions :tor a. conversion period in theA range about 4 to 20hours such that the rate of carbon deposition upon the catalyst declinesto a substantially constant value so that the ratio o! posited on thecatalyst, said gasoline and gas being at least in the range about 20 to30% by weight of the charge, discontinuing the flow of thie hydrocarboncharge through the contact mass lafter substantial deposition of carbonupon the catalyst, reactivatng the catalyst in situ, and then repeatingthe process.

l0. In the catalytic cracking of a normally liquid heavier hydrocarbonoil charge to convert the same to gasoline hydrocarbons involvingalternate periods of conversion of the oil and reactivation of thecatalyst, wherein a vaporized feed oil, having a carbon residue of lessthan 0.2% and a color of less than 200 on the Lovibond 1/z inch scale,at a temperature oi 910 to 1050 F. and at high space velocity in therange 3 and above, isvcontinuously passed through an active contact massmaintained at the elevated temperature during said periods ofconversion, the method comprising continuing the flow of heated chargeoil through the contact mass under said conditions for a conversionperiod of about 4 hours such that the rate of carbon deposition upon thecatalyst declines to a substantially constant value so that the ratio ofgasoline plus gas to carbon being produced when the catalyst has beenonstream 4 hours or more is substantially greater than that obtainingduring a period of less than 4 hours, obtaining a conversion yield togasoline plus gas of about at least 50 pounds per pound of carbondeposited on the catalyst, said gasoline and gas being at least in therange about 20 to 30% by weight of the charge. discontinuing thg dow oithe hydrocarbon charge through the contact mass after substantialdeposition of carbon upon the catalyst, reactivating the catalyst insitu, and then repeating the process.

11. In the catalytic cracking oi normally liquid hydrocarbon oil toconvert the same to gasoline hydrocarbons involving alternate periods ofconversion oi the oil and reactivation oi the catalyst, wherein avaporized feed oil, having a carbon residue of less than 0.2% and acolor of less than 20o on the Lovibond 1/2 inch scale, at a temperaturein the range of about 910 to 1050 F. and at high space velocity in therange oi about 3 to 10,

. is continuously passed through an active contact mass maintained atthe elevated temperature during said periods of conversion, a methodcomplising continuing the :dow of heated charge oil through the contactmass anders dconditions ior-4 a conversion period in the range about 4to 30 hours to obtain a conversion to gasoline plus gas of atleast aboutpounds per pound of carbon deposited on the catalyst, the ratio ofgasoline plus gas to carbon being produced when the catalyst has beenonstream 4 hours or more being substantially greater than that obtainingduring a period of less than 4 hours, then discontinuing the flow of thehydrocarbon charge in contact with said catalyst after substantialdepositionV of carbon upon the catalyst, reactivating the catalyst insitu, and then repeating the process.

DU BOIS EASTMAN. CHARLESRICHKEIR..

